2000 Silverado 2500HD 4x4 6.0L - Brake issues

Hey All, Im a Newbe, so forgive me if I started this in the wrong place. I am having issues with my Brakes. I had a full peddle one day on the way home from work and the peddle went to the floor and then came back when I tried again. Then the other day they went to the floor almost and only the front brakes are now working. I have a lift, so I checked under the truck and found no leaks, the reseivor is full! The pump for the booster is full. My first through was the booster, so does anyone now of a test to insure I am going in the right direction? Thanks for your help!

Welcome to GMTC! I have a few questions to ask about your brake issue. Is the master cylinder full of fluid? Open it and take a look inside, is it full all the way across? I ask this because the inside of the reservoir is divided into 2 sections. Now look where the master cylinder mounts to the brake booster, do you see any fluid there (at the mounting point)? Does your truck have a hydrobooster or a vacuum booster? Are there power steering lines running to the booster or does it look like a pancake style air compressor?

Thanks for your reply, I have a full reservoir, I haven't checked the mounting point for leaks, but I will do so, and I have a hydrobooster and the reservoir for the hydrobooster pump is full too. I feel the Master cyclinder is the problem at this point. I have order a new one, I will let you know if this has resolved my problem. Thanks again for your reply.

to test the hydro booster, shut the truck off, pump the pedal 10 times, hold the pedal down and start the truck. The pedal should push back against your foot if the hydrobooster is working properly. I am looking for the document now, but there was a recall on certain year 2500 models due to a bad valve in the hydro boost that caused the issue that you are describing.

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the recall only effected 2004-2005 models. I would look for a brake line bulging.